The phrase “Microelectromechanical systems” or MEMS generally describes the technology of very small devices. Conventionally MEMS are made up of components between 1 to 100 micrometers in size (i.e. 0.001 to 0.1 mm), and more typically range in size from 20 micrometers (20 millionths of a meter) to a millimeter (i.e. 0.02 to 1.0 mm). They usually consist of components that interact with the outside world such as microsensors. At these small sizes MEMS raise different technological challenges. For example, because of the large surface area to volume ratio of MEMS, surface effects such as electrostatics and wetting dominate over volume effects such as inertia or thermal mass.
MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics. These include molding and plating, wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electro discharge machining (EDM), and other technologies capable of manufacturing small devices.
In some embodiments disclosed herein, light may be used to force electrons from the surface of a solid. This process is generally referred to as the photoelectric effect (or photoelectric emission or photoemission). A material that can exhibit this phenomena is said to be photoemissive, and the ejected electrons are sometimes called photoelectrons. The major factors affecting the kinetic energy of photoelectrons are the frequency of the incident radiation and the material on the surface.